This invention relates to a water injection propulsion device and more particularly to improved jet propulsion unit and drive therefore for a watercraft.
The use of water jet propulsion units for watercraft is well known and has a number of advantages over more conventional propeller type watercraft. However, in order to permit the use of a small compact propulsion unit, it is desirable to employ an engine that operates at a high speed range. As is well known, the higher of operational speed of the engine, the greater the power output for a given size. However, if the jet propulsion unit is driven at too high a velocity, its efficiency may decrease due to cavitation in the pumping system.
In order to avoid these problems, it has been proposed to utilize a speed reduction transmission of some form between the engine output shaft and the impeller shaft of the jet propulsion unit. This permits the engine to be driven at a high speed so as to achieve a high output for a low displacement but also insures that the impeller of the jet pump will not be driven at too high a speed so as to lose efficiency due to cavitation. However, the devices previously proposed for this purpose have required the interpositioning of a separate transmission between the engine output shaft and the impeller shaft. This adds to the number of couplings in the drive and further gives rise to problems in mounting in order to assure accurate alignment of the engine output shaft, the transmission shafts and the impeller shaft.
It is, therefore, a principal object to this invention to provide an improved water injection propulsion device for a watercraft.
It is a further object to this invention to provide a water injection propulsion system for a watercraft having a high speed engine with an integral speed reducing transmission formed as a part of one of the engine or the jet propulsion unit.
It is a further object to this invention to provide an improved water injection propulsion system wherein a speed reducing transmission is incorporated directly in the driving engine of the watercraft so as to avoid the necessity of separate couplings and minimize alignment difficulties.